The present invention relates to an ink jet recording apparatus which, in accordance with an image signal input therein, generates a print signal in such a manner that a plurality of color inks are dot printed repeatedly at a unit pixel, and records gradations by the respective colors, thereby recording a color image.
Conventionally, as an ink jet recording apparatus capable of gradation recording, as disclosed in the Unexamined Japanese Patent Application Publication Nos. Sho 55-79162, Hei 4-361049, Hei 7-323536 and the like, there is known an ink jet recording apparatus of a type in which, a plurality of ink dots are applied or printed at the same position on a record medium. However, in the high optical density portion of the printing, since ink dots are printed many times repeatedly, the amount of ink on the record medium is large. Therefore, unless there is used a record medium having a large ink holding capacity, the ink can be blurred or can soak into the back surface of the record medium. In these citations, there is shown a case in which only one kind of color ink is used. However, for example, when carrying out a color print, two to four colors inks are applied to the same position: that is, in the color print, the above-mentioned problem relating to the blurred ink and soaked ink becomes more serious.
In order to improve the above problems, for example, as disclosed in the Unexamined Japanese Patent Application Publication No. Sho 60-153669, there is proposed a system in which, after ink dots are forcibly dried, other ink drops are applied repeatedly at the same position. However, in this system, the forced drying requires a heater or the like, which increases the cost of the system.
Also, as another gradation recording system, for example, as disclosed in the Unexamined Japanese Patent Application Publication Nos. Sho 61-108254, Hei 3-5161, Hei 5-38818, and the like, there is known a system in which gradations are expressed using at least two kinds of, that is, dense and light inks for the same color. According to this method, in the high optical density portion, instead of printing by applying the ink dots repeatedly onto the same position on a record medium, the dense ink is substituted for the light ink for printing, which can reduce the amount of ink applied onto the record medium over the previously described conventional system: that is, there hardly arises the problem that the ink can be blurred or can soak to the back surface of the record medium. However, use of this system increases the kinds of inks used, which makes it difficult to reduce the cost of the ink jet recording apparatus using this system.
The present invention aims at eliminating the above-mentioned problems found in the conventional ink jet recording apparatus. Accordingly, it is an object of the invention to provide an ink jet recording apparatus which, when printing a high optical density portion of a color image or applying a large number of inks at the same position, can reduce the possibility that the ink can be blurred and ink can soak to the back surface of the record medium.
When printing an image signal, one or more colors are used according to the image signal. For every color used, ink dots are printed repeatedly by the number that corresponds to the number of times of repeated printing, thereby printing the image signal or a color image. Normally, there is decided the maximum number of times of repeated printing that is the number of dots when printing a color image at a maximum optical density. In the normal printing, in order to print a color image at a maximum optical density, dots, which are equal in number to the addition value or sum of the maximum numbers of times of repeated printing by colors used, are printed repeatedly at a unit pixel. In this case, as previously described, there is the possibility that the ink can be blurred and can soak to the back surface of the record medium. In view of this, according to the invention, the maximum dot number that can prevent the occurrence of such blurred and soaked ink is set as a given value; that is, the maximum numbers of times of repeated printing for the respective color are limited so that the addition value or sum of the maximum numbers of times of repeated printing for the respective colors used can provide a limited repeated printing conversion number equal to or less than the given value. In this case, ink amount limiting coefficients, which are coefficient for limiting the ink amounts of the respective colors, are calculated using ink amount limiting coefficient calculating means. And, in accordance with the image signal and ink amount limiting coefficients, a print signal is generated by a print signal generating means. Due to this, the print signal is limited to the limited repeated printing conversion number even when the number of times of repeated printing for each color is set largest, thereby being able to reduce the possibility that the ink can be blurred and can soak to the back surface of the record medium.
When finding the ink amount limiting coefficient by use of the ink amount limiting coefficient calculating means, the ink amount limiting coefficient can be calculated in accordance with the sum of the numbers of times of repeated printing for the respective colors when the image signal is printed as it is; that is, for example, when the added value or sum of the number of times of repeated printing for the respective colors is equal to or less than the limited repeated printing conversion number, the ink amount limiting coefficient can be used as a value which has no influence in the above-mentioned print signal generating means; or, the added value of the number of times of repeated printing for the respective colors is weighted so that the added value of the maximum numbers of times of repeated printing provides the limited repeated printing conversion number, thereby being able to find the above-mentioned ink amount limiting coefficient from which the weighted numbers of times of repeated printing can be obtained.
Also, the print signal generating means is able to multiply the components of each of the colors of the image signal by the ink amount limiting coefficients for the respective colors to thereby generate a print signal; and, the portions of the color components of the image signal which are common to two or more of the color components of the image signal can be multiplied by the above-mentioned ink amount limiting coefficients corresponding to the common portions to thereby generate a print signal, whereas the other or excess portions thereof not common can be added together as they are to thereby generate a print signal.
Further, such limitation of the ink amount can be executed selectively according to printing modes. Also, a print signal to be output can be halftone processed before it is printed. Further, there can also be employed a structure that the variations in the colors caused by the processing by the image signal generating means can be previously corrected by color correcting means.